It's hard to find good pictures where you can see the seats. I'm posting links to pictures, because the ones with enough detail are also too large to post directly.
Here's a Dexstar wheel "like" redracers. You can see how the area around each stud hole is raised as part of forming the seat.
picture And here's a different brand, where you can easily see that the holes are beveled to match the cone nuts.
picture I don't claim that's the case for
all trailer wheels. China makes a lot of cheap ****. But any decent lug centric wheel will have beveled seats. The original claim that "steel wheels do not have a chamfered shoulder..." is definitely not true.